Means for transient damping of an ignition coil



July 16. 1968 0. K. NILSSEN 3,392,716

MEANS FOR TRANSIENT DAMPING OF AN IGNITION COIL Filed July 20, 1966 3 Sheets-Sheet 1 FIG.3

INVENTOR Arrow/vs July 16. 1968 0. K. NILSSEN 3,392,716

MEANS FOR TRANSIENT DAMPING 0F AN IGNITION COIL Filed July 20, 1966 5 Sheets-Sheet 2 FIG.5

FIG 4 INVENTOR 01.5 A. lV/4 68! BV 2 6 1' 744.14% d6 ATTORNZS July 16, 1968 0. K. NILSSEN 3,392,716

MEANS FOR TRANSIENT DAMPING OF AN IGNITION COIL Filed July 20, 1966 5 Sheets-Sheet 3 F'IG.8

INVENTOR 41' K. A04 66f ATTOR/V VS United States Patent 3,392,716 MEANS FOR TRANSIENT DAMPING OF AN IGNITION COIL Ole K. Nilsseu, Livonia, Micl1., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed July 20, 1966, Ser. No. 566,595 8 Claims. (Cl. 123-448) v ABSTRACT OF THE DISCLOSURE An ignition system in which the peak transient voltage present in the secondary winding of an ignition coil when transformed to the primary winding as the primary wind ing is energized is limited to the terminal voltage of the source of electrical energy. This is accomplished through the use of a resistor coupled in circuit with the source of electrical energy, the switching means of the ignition system and the primary winding. A saturable inductor is connected in parallel with this resistor and it is designed to have a very large inductive reactance when initially energized compared to the resistance of the resistor and to reach saturation when the voltage on the secondary winding transformed to the primary winding reaches the value of the terminal voltage of the source of electrical energy. Additionally, the value of the resistor may be adjusted to provide critical circuit coupling and the parallel circuit comprising the resistor and saturable inductor has negligible impedance when the saturable inductor is saturated.

This invention relates to means for transient damping of an ignition coil of an ignition system for use in an internal combustion engine.

In an internal combustion engine ignition system, the moment the primary winding of the ignition coil is connected to a source of electrical energy a transient voltage is induced in the secondary winding of the coil. This is normally of oscillatory form due to the inductance and the distributed capacitance of the ignition coiLThe peak transformed secondary voltage, that is, the voltage induced in the secondary winding transformed to the primary winding may reach at least twice that of the terminal voltage of the source of electrical energy.

The oscillatory voltage induced in the secondary winding upon the closing of the switching system connected to the primary winding occurs in both conventional and transistorized ignition systems. However, the fewer the number of turns on the primary winding (assuming a given primary voltage and a given number of secondary turns) the larger this transient voltage induced in the secondary winding will be. Conventional ignition coils have some 250 turns on the primary and 25,000 turns on the secondary, and the secondary voltage transients may reach peaks of 2.5 kilovolts. This is normally not large enough to cause any trouble or preignition in the internal combustion engine.

Transistorized ignition systems, however, use primary windings with 100 turns or less and the secondary transient voltages may reach 6 kilovolts and more when the primary winding is energized. With this high a voltage present, the spark plugs coupled to the secondary winding may break down prematurely, that is, during the charging rather than the discharging of the ignition coil. Such preignition has been observed and does constitute a problem in transistorized ignition systems. This is particularly true with transistorized ignition systems in which the primary winding may be connected directly to the source of energy for only a very short period of time prior to the firing of the spark plugs.

In order to prevent the peak oscillatory transient voltage present in the secondary winding as the primary winding is energized from causing pre-ignition, its value should be substantially lowered. This may be accomplished by limiting the peak oscillatory transient voltage present in the secondary winding when transformed to the primary winding, to the terminal voltage of the source of electrical energy through the use of a resistor inserted in series with the source of electrical energy and the primary winding. Its value should be adjusted to provide critical circuit damping. With such a resistor, however, the current in the primary winding of theignition coil will normally be limited to a lower value than desired. The present invention remedies this ditliculty by providing a saturable inductor connected in parallel with this series resistor that provides critical circuit damping. The saturable inductor is designed to have a very large inductance reactance compared to the resistance of the resistor and to reach saturation when the voltage on the secondary winding, transformed to the primary side, reaches the value of the terminal voltage of the source of electrical energy. When the saturable inductor does reach saturation its impedance becomes negligible and this permits a large current flow in the primary winding, thereby permitting large secondary voltages to be generated in the secondary to fire the spark plugs when current in the primary winding is interrupted.

An object of the present invention is the provision of a means for transient damping of a transformer, particularly an ignition coil of an ignition system, when the primary winding is initially connected to a source of electrical energy, with this means including means for permitting a proper amount of current to flow into the primary winding subsequent to this transient damping.

A further object of the invention is the provision of an ignition system for an internal combustion engine which will prevent premature firing of the spark plugs, but will at the same time permit sufficient current to flow in the primary winding so that adequately high secondary voltages will be generated in the secondary winding of the coil to fire the spark plugs at the proper time in the ignition cycle.

Other objects and attendant advantages of the present invention will be more readily realized as the specification is considered in connection with the attached drawin gs, in which:

FIGURE 1 is a circuit diagram of an ignition system employing the present invention;

FIGURE 2 is a circuit diagram of another ignition system employing the present invention;

FIGURE 3 is an equivalent circuit of an ignition coil used in a conventional ignition system that does not employ the present invention;

FIGURE 4 is a waveform of the voltage appearing across the secondary winding of the ignition coil used in a conventional ignition system transformed to the primary side as a function of time when the primary winding is initially energized;

FIGURE 5 is an equivalent circuit of an ignition coil for an ignition system employing the present invention;

FIGURE 6 is a hysteresis loop of the saturable inductor used with the present invention;

FIGURE 7 is a curve showing the voltage induced in the secondary winding of the ignition coil in which the present invention is employed when transformed to the primary side upon the initial energization of the primary winding; and

FIGURE 8 is a curve showing the charging current in the primary winding of an ignition coil of the ignition system employing the present invention.

Referring now to FIGURE 1, there is shown an ignition system which includes the transient damping means of the present invention in which an ignition coil 10 has a primary winding 11 and a secondary winding 12.

The se'condarywinding 12 is connected through read 13 .toa re ating arm 14 Q.f..a..dit yt 1. th tha a plurality of spaced contacts 15. The rotating arm 14 sequentially comes into electrical contact with the contacts 15. and this sequentially connects a plurality of spark plugs 17 to thesecondary winding 12 of the ignition coil through the lead 13, the rotating arm 14, the spaced contacts 15, and leads. 18, 19, 20, 21, 22 and 23.

The primary winding 11 of the ignition coil 10 is connected to the negative terminal 26 of a source of electrical energy or storage battery 27 through leads 28 and 31 and a parallel circuit of a resistor 29 and a saturable inductor 30. The other terminal of the primary winding 11 of ignition coil 10 is connected to an output electrode 32, in the form,of a collector, of a solid state switching device preferably in the form of transistor 33. The other output electrode 34 .of this solid state switching device or transistor 33, shown in the form of an emitter, is connected to the positive terminal 35 of the source of electrical energy or battery 27 through lead 36, lead 37 and lead 38.

A saturable switching core 41 is employed to control the conduction of the solid state switching device or transistor 33. This saturable switching core has a first winding 42 having its dot marked terminal connected to the positive terminal 35 of battery 27 through lead 43, resistor 44, lead 40, lead 37 and lead 36. The other end of the winding 42 is connected through lead 45, with contact 46 of ignition contact breaker points 47. The other contact 48 is connected to the lead 31 through a movable arm 51. The ignition contact breaker points 47 are normally biased to a closed position, and are separated or opened periodically by a cam 54 that operates a follower 55 coupled to the arm 51. This cam is operated in synchronism with the rotatable arm 14 of the distributor 16 as shown by the dotted line 56, and it is arranged so that the ignition contact breaker points 47 open just shortly before the rotating arm 14 makes contact with contacts that are connected to the leads 18 through 23 respectively.

' The saturable switching core 41 also has a second winding 61 wound thereon that has its dot marked terminal coupled to lead 31 via lead 62 and the other end connected through lead 63 to the ignition coil 10 and the output electrode or collector 32. of the solid state switching device or transistor 33. It can be appreciated, therefore, that the winding 61 is connected directly across the primary winding 11 of ignition coil 10, and is connected in parallel with the primary winding 11 in relation to current flow through the solid state switching device or transistor 33. A third winding 65 in the form of a feedback winding has its dot marked terminal connected through lead 66 to a control electrode or base 67 of the solid state switching device or transistor 33, while the other end of the winding 65 is connected through lead 68, resistor 71, lead 72, lead 37, and lead 38 to the output or emitter electrode 34 of the solid state switching device or transistor 33.

A capacitor 73 is connected across the primary winding 11 of ignition coil 10 for the usual purposes of preventing too rapid a rise in the voltage in the primary winding 11 as the solid state switching device or transistor 33 is de-energized. This furnishes protection for the transistor against reverse voltages that may be so high as to destroy its operating characteristics. A diode 75 is positioned in lead 62 to prevent repetitive sparking.

In operation of the circuit shown in FIGURE 1, with the contacts 46 and 48 of the ignition contact breaker points 47 closed, a circuit will be established through the first winding 42 on the saturable switching core 41 from the source of electrical energy or battery 27. The resistance of this circuit, including the resistance of resistor 44 and the resistance of the winding 42, is such that the number of ampere turns or volt seconds applied to the core 41 is such to bias it into a negative state of saturation. At this time, the solid state switching device or transistor 33 will be in a nonconducting state because no voltage will be developed at this time across the feedback winding'65, ahd the emitter 34 and the base will beat the same potential. Since the solidstate switching device 33 is in the nonconducting state, there will be no current flow through the primary winding 11 of the ignition coil 10 nor through the winding 61 of the saturable switching core 41.

It should be noted that with the dot conventionemployed here, current into a dot marked terminal will produce a magnetizing force to drive the core :toward =a-negative state of saturation while current into an unmarked terminal will produce a magnetizing force to drive the core toward a positive state of saturation' Similarly, a flux change from a negative flux state toward a positiveflux state will produce a negative voltage at a dot marked terminal of a winding with respect to its unmarked terminal and a flux change from a positive flux state toward a negative flux vstatewill produce a positive voltage at a dot. marked terminal of a winding with respect to its unmarked terminal. When the ignition contact breaker points 47 open under the action of the cam 54 and follower 55, the bias on the saturable switching core will be removed and the flux level will fall to the negative remnant flux IeVCLThiS changing flux will induce in the feedback winding 65 a negative potential at the dot with respect to the potential at the other end of the winding 65. This will turn the transistor to a conducting state, and provide current flow through the primary winding 11 of the ignition coil 10 and through the winding 61 connected in parallel with the primary winding 11; Since current flows into the unmarked terminal of winding 61, the core will be switched toward a positive state of saturation and a negative potential will be produced at the dot marked terminal with respect to the unmarked terminal of feedback winding 65, thereby turning the transistor to its fully conducting state by virtue of this feedback action. Current through winding 61 pr0- vides sufficient magnetizing force on the saturable switching core 41 to drive it fromthe negative remnant flux level into a positive saturated condition.

When the saturable switching core reaches the positive saturated state, the feedback voltage in the winding 65 will fall to zero thereby turning off the transistor or solid state switching device 33 and interrupting thecurrent flow through the primary winding 11 of ignition coil 10. This interruption of the current flow will induce a voltage in the primary winding 11 and a stepped up ig nition voltage in the secondary winding 12 which will be applied at this time to one of the spark plugs through the lead 13, the rotatable arm 14, one of the contacts 15, and one of the leads 18 through 23 of the distributor 16. This voltage willalso act on the winding 61 through diode to move the core 41 to a stable position of residual flux, i.e., a positive state of remnant flux. As soon as the contacts 46 and 48 of ,the ignition contact breaker points 47 close, the magnetization of the core will be switched back to a negative state of saturation and another ignition cycle will occur only when the contacts 46 and 48 of the ignition contact breaker points 47 open.

The ignition system described above and shown in FIGURE 1 without the resistor 29 and saturable inductor 30 is described and claimed in my copending application Ser. No. 403,263, filed Oct. 12, 1964.

Another transistorized ignition system in which the present invention may be used is shown in FIGURE 2. In this ignition system, the negative terminal 26 of the source of electrical energy or storage battery 27 is connected to ground through a lead 28. The positive terminal 35 is connected to emitter '34 of transistor 33 through a lead 36, while the collector 32 is connected to the parallel circuit comprising the resistor 29 and the saturable inductor 30, and this saturable inductor 30 and resistor 29 are connected to the primary winding 11 of the ignition coil 10. The base 67 of the transistor 33 is connected to contact 48 of ignition contact breaker points 47 through a lead 81 and resistor 82. The other contact 46 of the ignition breaker points 47 is connected to ground through a lead 83, A resistor 84 inter-connects the emitter 34 and the base 67 to provide a rapid cut-off of the transistor 33 when the contacts 46 and 48 are opened. A protective Zener diode '86 is positioned between the collector and emitter of transistor 33 to prevent high transient voltages from injuring the transistor 33.

The ignition system of FIGURE 2 operates in the following manner. When the contacts 46 and 48 are closed, a proper bias is applied to the emitter 34-base 67 circuit of the transistor 33 switching it to its conducting state. Current therefore flows from the source of electrical energy 2.7 through lead 36, emitter 34 and collector 32 ofthe transistor 33 and through the parallel combination of the resistor 29 and saturable inductor 30 to the primary winding 11 of the ignition coil 10.

At this time, the arm 14 of the distributor 16 will be at some position intermediate the contacts 15 positioned on the distributor. When the rotating arm 14 nears or is in contact with one of these contacts 15, the contacts 46 and 48 of ignition contact breaker points 47 open through the action of the cam 54 and follower 55 thereby switching the transistor 33 to its nonconducting state and interrupting current in the primary winding 11 of the ignition 10. This causes generation of the necessary high voltages in the secondary winding 12.

. The particular purpose and operation of the saturable inductor 30 and resistor 29 in both the circuits of FIG- URES 1 and 2 will be explained subsequently. In order to understand the operation and purpose of these components it is desirable to consider an ignition system which does not employ them. The equivalent circuit for an ignition coil that does not use these components is shown in FIGURE 3 with the switch designatedv by the letter S being equivalent to the transistor 33 in either of the circuits shown in FIGURE 1 or 2. The equivalent inductance of the primary coil L-M and the transformed inductance of the secondary coil L2'-M are shown connected in series with the transformed distributed capacitance C of the secondary winding. The mutual inductance of the primary winding and the secondary winding is designated by the letter M, and the voltage E is the voltage developed across the secondary winding transformed to the prim'aryvside when the switch S is initially closed. The voltage source E, is, of course,.the source of electrical energy or storage battery 27 of FIGURES 1 and 2 of this application.

The voltage waveform E that develops in the secondary winding transformed to the primary winding when the switch S is closed is shown in FIGURE 4. This voltage waveform is of oscillatory shape due to the inductances and capacitance shown in FIGURE 3. The damping of this oscillatory waveform is due to the resistance present in the primary circuit of the ignition coil.

The value of E which is the voltage generated in the secondary winding transformed to the primary side, may be close to twice the terminal voltage E, of the source of electrical energy or storage battery 27 shown in FIG- URES 1 and 2. In transistorized ignition systems, an ignition coil with a turns ratio of'250 to 333:1 is ordinarily employed. It can be seen that with a terminal voltage of the battery or source of electrical energy 27 being in the range of 12 to 16 volts, that a very high transient voltage may be generated in the secondary winding when the switch S is closed. These secondary transient voltages may range from 6 to -kilovolts, and over 8 kilovolts has been actually observed when a 75 turn primary winding has been used in a transistorized ignition system. This may cause the spark plugs to break down prematurely during the charging of the primary windings rather than the discharge of the ignition coil. Such preignition has been observed and does constitute a problem in transistorized ignition systems, particularly with that disclosed in FIGURE 1 in which the primary winding is coupled to the source of electrical energy only a short time prior to the requirement for ignition voltages. In that case, the rotatable arm 14 may be very near or in contact actually with the contacts 15 on the distributor at the time of the connection of the source of electrical energy to the primary winding.

The present invention provides a means for not only lowering this transient voltage that is generated in the secondary winding when the primary winding is connected to the source of electrical energy, but it also permits sufiicient electrical current to flow into the primary winding to build up sufficient flux that the flux change upon interruption of this primary current will generate the necessary ignition voltages in the secondary winding. To do this, the resistor 29, in combination with the parallel saturable inductor 30, is employed. To prevent the oscillatory type waveform from being induced in the secondary winding of the ignition coil, the resistance should be selected so that its value provides critical circuit damping. The saturable inductor is designed to provide a very large initial inductive reactance when the switch S is closed compared to the resistance of the resistor 29. It is also designed to reach saturation at the moment the voltage induced in the secondary winding transformed to the primary side reaches the value E, of the terminal voltage of the source of electrical energy 27 and preferably to have a very small resistance compared to the resistance of the above-mentioned damping resistor.

The equivalent circuit for the ignition coil 10 of either the ignition system shown in FIGURE 1 or FIGURE 2 is shown in FIGURE 5. Normally, the transformer coupling between the primary winding and the secondary winding is high, approximately which means that the mutual inductance M is much larger than the other two inductances L M and Lg-M shown in the equivalent circuit. The values, therefore, of the inductive reactance of this mutual inductance and the value of the inductive reactance of the saturable inductor are so high initially, i.e., when the switch S is first closed, that they may be disregarded in the circuit. In other words, the circuit components L and M would be equivalent to open circuits when the switch S is initially closed. The resistor R should be selected to provide critical damping in the remaining circuit.

The circuit described in the preceding paragraph provides the waveform shown in FIGURE 7 in which the induced voltage E in the secondary winding when transformed to the primary side is not of oscillatory form, but only rises to the terminal voltage E, of the source of electrical energy 27. As stated previously, L or the saturable inductor 30 should be designed to reach saturation at the moment that E, reaches the value of E, at which time the current flowing into the capacitor C, shown in equivalent circuit of FIGURE 5, reaches zero. At this time, therefore, the saturable inductor L or 30 provides a short circuit essentially around the resistor R or 29 and since the saturated saturable inductor will have essentially negligible impedance, charging current, therefore, flows through this saturated inductance into the primary winding 11 of the ignition coil as represented by the mutual inductance M. Since the saturated saturable inductor L or 30 has essentially negligible impedance, the coil charging current, designated by I in FIGURE 8, will continue to rise sufliciently to generate proper ignition voltages in the secondary winding 12 when the transistor 33 in either FIGURE 1 or 2 is switched to its nonconducting state.

The hysteresis loop of the magnetic material employed in the saturable inductor L or 30 should be approximately that shown in FIGURE 6. As evidenced by the hysteresis loop, the magnetic material should have a low remnant flux density so that when current is interrupted in the primary winding of the ignition coil by the transistor 33 being switched to a nonconducting state, the saturable inductor L or 30 will return from its saturated condition represented by the dot to the point just above BH origin at a very low remnant flux density.

When the transistor is switched back to its nonconducting state and the saturable inductor returns from its saturated state to its stable point at a low remnant density, the ignition circuit is then ready for another cycle of operation.

The peak voltage, E the transformed voltage appearing across the secondary winding of the ignition coil when the primary winding is initially energized, is therefore cut substantially in half. As a result, the peak transient voltages induced in the secondary winding upon initial energization of the primary winding is also reduced by a factor of 2, so there will be no problem with pre-ignition resulting from this voltage being applied to the spark plugs.

The invention is particularly suited for an ignition system in which the primary winding is connected to the source of electrical energy only a short period of time prior to the requirement for ignition voltages. It is also useful in other standard and transistorized ignition systems, where the advance and retard mechanism of the distributor may bring the arm of the distributor in close proximity to its contacts 87 when the switching mechanism in the primary circuit connects a source of electrical energy to the primary winding.

It is to be understood that this invention is not to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An ignition system for an internal combustion engine comprising an ignition coil having a primary and a secondary winding with high transformer coupling and a high turns ratio between the primary winding and the secondary winding, a spark plug, a source of electrical energy, switching means operated in synchronism with the engine for periodically connecting and disconnecting said primary winding of said ignition coil to said source of electrical energy, and means coupled in circuit with said source of electrical energy, said switching means and said primary winding of said ignition coil for limiting the peak transient voltage induced in said secondary winding when transformed to the primary winding substantially to the terminal voltage of said source of electrical energy as said switching means connects said primary winding to said source of electrical energy and for connecting said primary winding to said source of electrical energy through a circuit having negligible impedance when said peak transient voltage in said secondary winding transformed to the primary side reaches the value of the terminal voltage of said source of electrical energy.

2. The combination of claim 1 in which said last mentioned means comprises a parallel circuit of a resistor and a saturable inductor connected in series with said source of electrical energy and said primary winding, said resistor having a resistance value selected to provide critical circuit damping and said saturable inductor has a very large inductive reactance compared to the resistance value of said resistor when said switching means initially connects said source of electrical energy to said primary winding and a negligible impedance when saturated.

3. An ignition system for an internal combustion engine comprising an ignition coil having a primary and a secondary winding with high transformer coupling and a high turns ratio between the primary winding and the secondary winding, a plurality of spark plugs, means for sequentially coupling said secondary winding of said ignition coil to said spark plugs in synchronism with the operation of the engine, a source of electrical energy, switching means operated in synchronism with the engine for periodically connecting and disconnecting said primary winding of said ignition coil to said source of electrical energy, and means coupled in circuitwith said source of electrical energy, said switching means and said primary winding of said ignition coil for limiting the peak transient voltage induced in said secondary winding when transformed to the primary winding substantially to the terminal voltage of said source of electrical energy as said switching means connects said primary winding to said source of electrical energy and for connecting said primary winding to said source of electrical energy through a circuit having negligible impedance when saidfipeak transient voltage in said secondary winding transformed to the primary side reaches the value of the terminal voltage of said source of electrical energy.

4. The combination of claim 3 in which said last mentioned means comprises a parallel circuit of a resistor and a saturable inductor connected in series with said source of electrical energy and said primary winding, said resistor having a resistance value selected to provide critical circuit damping and said saturable inductor has a very large inductive reactance compared to the resistance value of said resistor when said switching means initially connects said source of electrical energy to said primary winding and a negligible impedance when saturated.

5. A transistorized ignition system for an internal combustion engine comprising an ignition coil having a primary winding and a secondary winding with a high transformer coupling and a high turns ratio between said primary winding and said secondary winding, a spark plug, means coupling said spark plug to said secondary winding, a source of electrical energy, a transistor having an emitter a collector and a base, said emitter and collector being connected in circuit with said primary winding of said ignition coil and said source of electrical energy, means connecting the base of said transistor to said source of electrical energy and operated in synchronism with the engine for causing said transistor to be periodically switched between conducting and nonconducting states, and means coupled in circuit with said source of electrical energy, said emitter and collector of said transistor and said primary winding of said ignition coil for limiting the peak transient voltage induced in said secondary winding when transformed to the primary winding to substantially the terminal voltage of said source of electrical energy when said transistor is switched to a conducting state and for connecting said primary winding to said source of electrical energy through a circuit having negligible impedance when the peak transient voltage in said secondary winding transformed to the primary side reaches the value of the terminal voltage of said source of electrical energy.

6. The combination of claim 5 in which said last mentioned means comprises a parallel circuit of a resistor and a saturable inductor connected in series with said source of electrical energy, said primary winding and the emitter and collector of said transistor, said resistor having a resistance value selected to provide critical circuit damping and said saturable inductor has a very large inductive reactance compared to the resistance value of said resistor when said switching means initially connects said source of electrical energy to said primary winding and a negligible impedance when saturated.

7. An ignition system for an internal combustion engine comprising an ignition coil having a primary and a secondary winding, a plurality of spark plugs, means coupling said secondary winding with said spark plugs for sequentially connecting said spark plugs to said secondary winding in synchronism with the operation of said engine, a source of electrical energy, a transistor having an emitter, a collector and a base, a parallel circuit of a resistor and a saturable inductor, means connecting said primary winding, said emitter and collector of said transistor, said source of electrical energy and said parallel circuit of said resistor and said saturable inductor in series, means connecting said base of said transistor to said source of electrical energy to cause said transistor to conduct, and

means positioned in said last mentioned means and operated in synchronism with the engine for switching said transistor to a nonconducting state as said first mentioned means couples said secondary winding with said spark plugs, said resistor having a value to provide critical circuit damping and said saturable inductor having an inductive reactance sufliciently large that it is essentially an open circuit when said transistor is initially switched to a conducting state and saturates when the voltage induced in said secondary winding transformed to the primary winding reaches the value of the terminal voltage of said source of electrical energy.

8. An ignition system for an internal combustion engine comprising an ignition coil having a primary and a secondary winding, sadi ignition coil being constructed to provide high transformer coupling and a high turns ratio between the primary and secondary windings, a plurality of spark plugs, means for sequentially coupling said secondary winding of said ignition coil to said spark plugs in synchronism with the operation of the engine, a source of electrical energy, a switching means connecting said primary winding of said ignition coil in series with said source of electrical energy, said switching means including means operated in synchronism with the engine for connecting said primary winding of said ignition coil to said source of electrical energy and for disconnecting said source of electrical energy from said primary winding of said ignition coil when said first mentioned means couples said secondary winding of said ignition coil with said spark plugs, and means for preventing high transient voltages in the secondary winding of said ignition coil and for permitting current in said primary winding that is essentially unlimited by said means connected in series with said source of electrical energy, said switching mechanism and said primary winding of said ignition coil, said last mentioned means comprising a parallel circuit of a resistor and a saturable inductor, said saturable inductor having a very large inductive reactance compared to the resistance value of said resistor when said switching mechanism initially connects said source of electrical energy to said primary Winding and saturates when the transformed voltage across said secondary winding of said ignition coil reaches a value substantially equal to the terminal voltage of said source of electrical energy, said resistor having a value providing critical circuit damping for said ignition coil.

References Cited UNITED STATES PATENTS 1,598,192 8/1926 Seymour et al. 318239 XR 3,264,521 8/1966 Huntzinger et al. 3l5--224 3,304,926 2/1967 Maiden et a1. 3,312,210 4/1967 Nilssen.

FOREIGN PATENTS 186,389 10/ 1922 Great Britain.

LAURENCE M. GOODRIDGE, Primary Examiner. 

